1. Technical Field
Embodiments of the present invention relate to a sheet conveying device that conveys a sheet of recording material and an image forming apparatus including the sheet conveying device.
2. Related Art
Image forming apparatuses such as copiers such as digital copiers, printers such as laser printers, facsimile machines, and so forth include a sheet tray that accommodates a stack of sheets, so that the sheets are picked up and fed one by one to an image forming device. A sheet conveying device is used to feed the sheets one by one. This sheet conveying device includes a sheet separation/feeding mechanism employing a friction pad system, a FRR (friction reverse roller) system, or a corner separator system for separating and feeding a sheet of recording material.
A sheet conveying device employing the friction pad system includes a friction pad that functions as a friction member biased by a spring or other biasing member. The friction pad is pressed against an outer circumferential surface of a sheet conveying roller that functions as a rotary conveying member and is configured to prevent feeding of a sheet or sheets subsequent to an uppermost sheet picked from the sheet tray by the sheet conveying roller. Such a friction pad system is widely used because of its simple configuration that accepts various sheets having different widths.
Japanese Patent Application Publication No. JP 2005-343582-A discloses a sheet conveying device having a friction pad system. The sheet conveying device of JP 2005-343582-A includes a pair of projection members disposed laterally at both lateral end portions of a friction pad holder disposed downstream from a separation nip area formed between a sheet conveying roller and a friction pad. The pair of projection members lifts a sheet that has passed the separation nip area so as to avoid interference of the sheet with lateral end portions of a friction pad, preventing the sheet from having streaks and/or turnover thereon.
Japanese Patent Application Publication No. JP 2004-189350-A discloses another sheet conveying device having a friction pad system. In the sheet conveying device of JP 2004-189350-A, a center part of a friction pad to which a sheet conveying roller contacts is formed lower than both end parts of the friction pad to which sheet conveying roller does not contact, thereby forming a recess at the center portion and steps at the end parts (left and right). The steps cause the left and right parts of the sheet conveying roller to lift the sheet, which prevents the sheet from slidably contacting with both end parts of the friction pad and occurrence of abnormal sound.
Japanese Patent Application Publication No. JP 2000-198560-A discloses yet another sheet conveying device having a friction pad system. In the sheet conveying device of JP 2000-198560-A, a center part of a friction pad included therein is formed by a material smaller in hardness than both lateral sides thereof and the friction pad is cut at both lateral sides at a downstream part of a separation nip area so as to provide different resistances in sheet conveyance in the width direction of the sheet. By so doing, non-feeding of thick paper and multiple feeding of thin paper can be prevented.